Record "cache" inodes to clear while CE is locked.

There are two situations where we need to clear cached data from
all users, including those whose CE storage might still be locked:

1. When PackageManager is clearing caches to try making room for
package updates.
2. When the device fingerprint changes, we need to clear code caches
for all apps.

To enable this, we now record the inode number of the "cache" and
"code_cache" directories in xattrs of the parent directory.  This is
just enough information to find the cache directories to enable
deleting files inside.  When preparing CE storage for an app, we now
create these two directories and immediately write the inode numbers.

Bug: 26056125
Change-Id: I7e442b0676a695acf962593469793a93b03c8aee